The automotive industry, including both cars and trucks, and the manufacturing community utilize drum brakes for their braking systems. The drum brake is known as an internal expansion brake and it includes a brake drum having an internal generally circular cylindrical braking surface. The brake drum normally rotates with the vehicle's wheel or with a rotating component of a machine tool. One or more lined brake shoes are located within the center of the circular cylindrical braking surface. The lined brake shoes have a web and a table. The web normally extends radially inward from the table. The table is a curved partially cylindrical member which provides a surface onto which is attached a sacrificial brake lining which is shaped to mate with the braking surface of the brake drum. The rotating wheel or component is stopped by radially extending the lined brake shoe such that the sacrificial brake lining frictionally engages the braking surface on the brake drum. The energy of the rotating wheel or component is dissipated by the frictional engagement between the braking surface of the brake drum and the brake lining on the lined brake shoe. Over time and use, the sacrificial lining is worn away and has to be replaced in order for the braking system to continue to function. Normally this involves the replacement of the lined brake shoe and the resurfacing of the braking surface of the brake drum. The worn lined brake shoe is not discarded, it is used as a core which is sent to a rebuilder who removes the old lining and replaces it with a new lining. The brake linings generally are circular-cylindrical segments which may be bonded, riveted or otherwise attached to the table of the brake shoe.
In one conventional method of manufacturing the curved brake linings, a press ram of a press is displaced downwardly toward a mold for shaping the material which is to be formed into the brake lining in the press. The cavity of the mold is formed into the shape of a circular cylindrical segment which is the desired shape for the finished brake lining. The composition of material which is to be bonded under heat and pressure to form the brake lining is introduced into this cavity during the closing of the mold. Prior art compositions have frequently been a fibrous mixture which is metered into the closed cavity. A sufficient amount of the material to form the brake lining is introduced into the cavity prior to the final closing of the cavity. The pressing of the mixture into the final shape for the brake lining is normally carried out in multiple pressing stages and the end product is generally desired to have a generally constant thickness and a desired density.
Another method of manufacturing the curved brake linings is to first mold a generally flat rectangular sheet of the lining material. The flat sheet is then formed into the curved shape by heating the sheet, placing it into a non-heated die and forming the flat sheet into the desired shape. The curved sheet is then cut to the desired size, if necessary, and then attached to the frame to make the brake shoe.
The prior art methods of manufacturing brake linings and lined brake shoes have met with commercial success in both the automotive and industrial applications. The continued development of the process has been directed towards more efficient methods of manufacturing higher quality brake linings and lined brake shoes, especially those used in industrial applications. The lined brake shoes for industrial applications have brake linings which are generally greater in thickness than similar parts in the automotive applications. The ability to successfully bend the curved segments of brake lining from flat stock decreases significantly with the increase in thickness of the material.